C. elegans (nematoda) by Richard Birnbaum
1. Classification/Diagnostic Characteristics
Caenorhabditis elegans is a multicellular eukaryote that has a functioning nervous system. C. elegans undergoes cell differentiation, a proccess that changes less specific cells into their fated structures that have a very specific function. They belong to the Eukaryotic domain, animal kingdom, Caenorhabditis gennus, and C. elegans species.
2. Relationship to Humans
Both humans and nematodes are multicellular animals with brains, both are eukaryotic organisms, and both have cell development because of cellular differentiation. This species of nematode is not a human parasite, but many other species are parasitic in humans and other mammals. Humans have found the complete genome of C. elegans, and have done much scientific testing in laboratories with C. elegans (474). The organism is also used as a model organism, allowing people to study diseases like polycystic kidney disease (PKD) that affect humans but in a laboratory environment (9).
3. Habitat and Niche
Nematodes live in soil (236). Also, nematodes are a predator and feed on protists, small animals, and other roundworms (474). C. elegans normally inhabit very small spaces between damp soil particles or in rotting vegetation, where it lives in a film of water and is held to solid surfaces by surface tension. (1)
4. Predator Avoidance
Three-celled ringed fungi have learned to trap nematodes (441). C. elegans is 1mm long and lives in soil, so C. elegans only has microscopic predators that live in soil too.
5. Nutrient Acquisition
Oral cavity opens into a muscular sucking pharynx also lined with cuticle. Digestive glands are found here and secrete enzymes that break down food. The pharynx opens directly into the intestines. Nutrients diffuse through the cuticle and gut.
6. Reproduction and Life Cycle
C. elegans have two sexes, male and self-fertilizing hermaphrodite. A hermaphrodite is a naturally occurring organism that has both characteristically female and male reproductive organs. Most C.elegans are hermaphrodites, few are male. The hermaphrodites first produce sperm and then produce egg which will be either fertilized by its own sperm or by the sperm of the male elegans. Once they are fertilized within two to three hours they hatch approximately twelve hours later. The worms develop into adults in four larval stages; this generally takes about three days when the temperature ranges.
Life Cycle: The cycle of a nematode occurs in stages, which four larval stages, an immature adult stage, and a sexually mature adult stage. The first stage larva hatches from an egg when environmental conditions are suitable for survival of the larva. Each stage lasts until the larva is constrained by its cuticle, at which point it undergoes molting, a process in which a new cuticle is synthesized and the old cuticle is shed. This occurs between each larval stage as well as between the fourth larval stage and the immature adult stage. The adult nematode then grows to the limit of its constraints of its cuticle, simultaneously developing into a sexually mature adult. (4)
(6).
7. Growth and Development
C. elegans matures in three days into its body that has a set number of cells (474). C.elegans is transparent and microscopic. During each of the four larval molts, C. elegans secretes a new cuticle that will cover its body, shedding the old one (13).
C. elegans development is unique as it can be characterized better than any other multicellular organism. The developmental pattern of each somatic cell is known, from the zygote to the adult worm in the C. elegans development stages. A scientist can identify any cell at any point in development, and know the fate of that particular cell. (12)
8. Integument
The nematodes thick multilayer cuticle sheds four times and is used for gas exchange and nutrient exchange (474). The body cavity is maintained at a high pressure relative to the outside; this pressure acting on the tough impermeable elastic cuticle gives C. elegans its rigidity. (1)
9. Movement
The 1mm worm moves by contracting longitudinal muscles in its unsegmented body (474).
C. elegans can either swim or crawl, but they cannot do both at the same time. They swim in liquid and crawl in dirt. Normally they can easily transition between the two. The ability to do this comes from serotonin and dopamine. By blocking either of the chemicals the organism can both swim and crawl but cannot transition from one to the other. (10)
10. Sensing the Environment
C. elegans has nerves in its body, such as the dorsal nerve (474). C. elegans contain an estimated 300 neurons, including sensory organs in the head mediating responses to taste, smell, temperature and touch. Despite a lack of eyes, C. elegans may have the potential to respond slightly to light. C. elegans have an anterior nerve ring with a ventral nerve cord running the length of the body, as well as a smaller dorsal nerve cord. (7)
11. Gas Exchange
Nematodes exchange oxygen through its multilayered cuticle and its one cell thick gut (474). They don't have a circulatory system, but gas exchange occurs through simple diffusion over the cell walls. They excrete gaseous wastes similarly through this process of simple diffusion (by concentration gradients). (8).
12. Waste Removal
Longitudinal muscles contract to send materials from the pharynx to the anterior end. Also, the food gets digested. Four cell types make up the excretory system in C. elegans; one pore cell, one duct cell, one canal cell, and a pair of gland cells. The canal cell functions to remove metabolic products and maintain salt balance (2)
13. Environmental physiology (temperature, water and salt regulation)
This roundworm lives in dirt, which is rich in nutrients and holds moisture.
14. Internal Circulation
C. elegans is small enough to survive by oxygen and nutrients diffuse through the cuticle and gut. Each cell in the body gets enough from the environment without the need of a circulatory system.
15. Chemical Control (i.e. endocrine system)
C. elegans molts four times at the end of each larval stage. This process stops once the C. elegans reaches the adult age. This process is controlled by the regulation of the pqn-47 protein, a chemical signal that is expressed once the C. elegans is at the end of one of its larval stages.
1. Classification/Diagnostic Characteristics
Caenorhabditis elegans is a multicellular eukaryote that has a functioning nervous system. C. elegans undergoes cell differentiation, a proccess that changes less specific cells into their fated structures that have a very specific function. They belong to the Eukaryotic domain, animal kingdom, Caenorhabditis gennus, and C. elegans species.
2. Relationship to Humans
Both humans and nematodes are multicellular animals with brains, both are eukaryotic organisms, and both have cell development because of cellular differentiation. This species of nematode is not a human parasite, but many other species are parasitic in humans and other mammals. Humans have found the complete genome of C. elegans, and have done much scientific testing in laboratories with C. elegans (474). The organism is also used as a model organism, allowing people to study diseases like polycystic kidney disease (PKD) that affect humans but in a laboratory environment (9).
3. Habitat and Niche
Nematodes live in soil (236). Also, nematodes are a predator and feed on protists, small animals, and other roundworms (474). C. elegans normally inhabit very small spaces between damp soil particles or in rotting vegetation, where it lives in a film of water and is held to solid surfaces by surface tension. (1)
4. Predator Avoidance
Three-celled ringed fungi have learned to trap nematodes (441). C. elegans is 1mm long and lives in soil, so C. elegans only has microscopic predators that live in soil too.
5. Nutrient Acquisition
Oral cavity opens into a muscular sucking pharynx also lined with cuticle. Digestive glands are found here and secrete enzymes that break down food. The pharynx opens directly into the intestines. Nutrients diffuse through the cuticle and gut.
6. Reproduction and Life Cycle
C. elegans have two sexes, male and self-fertilizing hermaphrodite. A hermaphrodite is a naturally occurring organism that has both characteristically female and male reproductive organs. Most C.elegans are hermaphrodites, few are male. The hermaphrodites first produce sperm and then produce egg which will be either fertilized by its own sperm or by the sperm of the male elegans. Once they are fertilized within two to three hours they hatch approximately twelve hours later. The worms develop into adults in four larval stages; this generally takes about three days when the temperature ranges.
Life Cycle: The cycle of a nematode occurs in stages, which four larval stages, an immature adult stage, and a sexually mature adult stage. The first stage larva hatches from an egg when environmental conditions are suitable for survival of the larva. Each stage lasts until the larva is constrained by its cuticle, at which point it undergoes molting, a process in which a new cuticle is synthesized and the old cuticle is shed. This occurs between each larval stage as well as between the fourth larval stage and the immature adult stage. The adult nematode then grows to the limit of its constraints of its cuticle, simultaneously developing into a sexually mature adult. (4)
7. Growth and Development
C. elegans matures in three days into its body that has a set number of cells (474). C.elegans is transparent and microscopic. During each of the four larval molts, C. elegans secretes a new cuticle that will cover its body, shedding the old one (13).
C. elegans development is unique as it can be characterized better than any other multicellular organism. The developmental pattern of each somatic cell is known, from the zygote to the adult worm in the C. elegans development stages. A scientist can identify any cell at any point in development, and know the fate of that particular cell. (12)
8. Integument
The nematodes thick multilayer cuticle sheds four times and is used for gas exchange and nutrient exchange (474). The body cavity is maintained at a high pressure relative to the outside; this pressure acting on the tough impermeable elastic cuticle gives C. elegans its rigidity. (1)
9. Movement
The 1mm worm moves by contracting longitudinal muscles in its unsegmented body (474).
- Movement patterns of C. elegans : http://www.youtube.com/watch?v=GgZHziFWR7M (3)
C. elegans can either swim or crawl, but they cannot do both at the same time. They swim in liquid and crawl in dirt. Normally they can easily transition between the two. The ability to do this comes from serotonin and dopamine. By blocking either of the chemicals the organism can both swim and crawl but cannot transition from one to the other. (10)10. Sensing the Environment
C. elegans has nerves in its body, such as the dorsal nerve (474).
C. elegans contain an estimated 300 neurons, including sensory organs in the head mediating responses to taste, smell, temperature and touch. Despite a lack of eyes, C. elegans may have the potential to respond slightly to light. C. elegans have an anterior nerve ring with a ventral nerve cord running the length of the body, as well as a smaller dorsal nerve cord. (7)
11. Gas Exchange
Nematodes exchange oxygen through its multilayered cuticle and its one cell thick gut (474). They don't have a circulatory system, but gas exchange occurs through simple diffusion over the cell walls. They excrete gaseous wastes similarly through this process of simple diffusion (by concentration gradients). (8).
12. Waste Removal
Longitudinal muscles contract to send materials from the pharynx to the anterior end. Also, the food gets digested. Four cell types make up the excretory system in C. elegans; one pore cell, one duct cell, one canal cell, and a pair of gland cells. The canal cell functions to remove metabolic products and maintain salt balance (2)
13. Environmental physiology (temperature, water and salt regulation)
This roundworm lives in dirt, which is rich in nutrients and holds moisture.
14. Internal Circulation
C. elegans is small enough to survive by oxygen and nutrients diffuse through the cuticle and gut. Each cell in the body gets enough from the environment without the need of a circulatory system.
15. Chemical Control (i.e. endocrine system)
C. elegans molts four times at the end of each larval stage. This process stops once the C. elegans reaches the adult age. This process is controlled by the regulation of the pqn-47 protein, a chemical signal that is expressed once the C. elegans is at the end of one of its larval stages.
Online References:
1. http://www.wormatlas.org/ver1/MoW_built0.92/description.html
2. http://www.wormatlas.org/ver1/handbook/excretory.htm
3. http://www.youtube.com/watch?v=GgZHziFWR7M
4. http://cal.vet.upenn.edu/projects/merial/Nematodes/nems_5.htm
5. http://animaldiversity.ummz.umich.edu/accounts/Caenorhabditis_elegans/
6. http://www.wormatlas.org/ver1/handbook/anatomyintro/anatomyintro.htm
7. https://www.cbs.umn.edu/research/resources/cgc/what-c-elegans
8. http://www.darwinsgalapagos.com/animals/nematoda_roundworms.htm
9. http://www.nature.com/scitable/topicpage/c-elegans-model-organism-in-the-discovery-464
10. http://blogs.scientificamerican.com/scicurious-brain/2011/12/05/one-chemical-makes-you-crawl-another-makes-you-swim-if-you-are-c-elegans/
11. http://www2.estrellamountain.edu/faculty/farabee/biobk/nematode.gif
12. http://avery.rutgers.edu/WSSP/StudentScholars/project/introduction/worms.html
13. http://www.ncbi.nlm.nih.gov/books/NBK20145/
Textbook References:
Principles of Life by Hillis, Sadava, Heller, Price (441-474)